A HVAC system can typically include a compressor, heat exchangers such as a condenser and an evaporator, and an expansion device forming a refrigeration circuit. Refrigerant vapor is generally compressed by the compressor, and then condensed into liquid refrigerant in the condenser. The liquid refrigerant is then expanded by the expansion device to become low-pressure low-temperature two-phase refrigerant and is directed into the evaporator; and the two-phase refrigerant can then exchange heat with a process fluid, such as air or water, in the evaporator. The two-phase refrigerant may be vaporized in the evaporator and return to the compressor. The process fluid may then be used for other purposes, such as for example cooling a space of a building.
The compressors of the HVAC system, such as a screw compressor, may be lubricated, for example, by oil. The oil can circulate in the refrigerant circuit along with the refrigerant.